1. Field to Which the Invention Relates
The invention relates to a press for the production of plates and similar articles. It comprises a rigid upper pressing punch, which is shaped in accordance with the interior shape of the plate or the like to be pressed, and with an elastic membrane, which seals the top of the cavity of the mold the membrane is held at its edge corresponding to the dimensions of the eventual plate, and is provided with an annular groove corresponding to the foot of the plate. On this membrane pulverulent porcelain composition is distributed in the limits as determined by the holding action and the cavity is filled under the membrane with a pressure medium, which after lowering the press punch, can place pressure on the pulverulent porcelain composition, distributed on the membrane, in the pressing position of the pressing punch.
2. The Prior Art
In a construction in accordance with German patent specification (Offenlegungsschrift) No. 2,307,496 the membrane is held horizontally perpendicularly to the direction of movement of the upper pressing punch and, on lowering this pressing punch, is deformed downwards to assume the desired eventual shape under the action of the pressure exerted on it. However, it has been found that even if this downward movement is supported from below by suction forces, it is not possible to ensure precisely defined and precisely definable stresses within the membrane, which are transmitted to the pulverulent porcelain composition placed on the membrane. This leads to an irregular plate or similar article. Furthermore on demolding, when the pressed plate or the like becomes detached from the mold because the membrane returns to its initial position, that is to say to its flat position, forces are exerted on the pressed plate or the like, which then has low inherent strength, leading to damage to the plate, at least in its foot part, even if they do not result in complete destruction of the plate or the like.